| 摘要 |
PROBLEM TO BE SOLVED: To avoid troubles such as the development of a useless loss time and the marring of a screw main body by a method wherein the easy and sure separation of the remainder of a screw head part is realized even when the screw head part breaks. SOLUTION: At the fore part of a centering shaft part 7, a safety breakage part 10, the diameter of which is made smaller than that of the centering shaft part 7 and which is the most easily breakable part when a stress is applied on a screw head part 2, is provided. At the same time, a seat ring 11, some part of which fits to the centering shaft part 7 and the axial length of which is longer than the safety breakage part 10, is installed at the front end of a screw main body part 4.
|
